Many medical procedures gain access to the inside of an anatomical cavity by using an implement such as a trocar, cannular or needle having a sharpened point to pierce or puncture the bodily tissues, muscles and membranes forming the cavity wall. A surgical needle, for example, connected to a catheter may be used to pierce a cavity (blood vessel, subarachnoid space, heat ventricle). After piercing the cavity, the needle is left in situ and used to inject or withdraw gaseous or liquid phase fluids from the cavity. Similarly, in several endoscopic procedures, a small incision may be made in the skin of a patient along the abdomen for example, and the sharp point of a larger penetrating implement such as a trocar of suitable length and diameter is inserted into the incision, and pushed until the point punctures the cavity wall. Then, a sleeve is slid over the exterior surface of the implement into the puncture wound to serve as a lining for preserving the shape of the passageway created by the implement. After the sleeve is in place, the implement may be withdrawn and an endoscope and operating instruments may be inserted via the sleeve to view and operate upon organs within the cavity.
Penetrating the wall of an anatomical cavity with a surgical puncturing instrument can be quickly done and, usually creates a small neat passageway providing communication to the interior of the cavity. While the sharp point of a penetrating implement is being pushed through a cavity wall, it encounters great resistance from the tissue, muscle and membranes forming the cavity wall. Once the sharp point and blade of the implement pass through the cavity wall and into the cavity, the resistance drops significantly. The sharp point of the implement, however, can easily injure organ structure within the cavity upon the slightest contact. Unless a surgeon stops pushing the implement just as soon as penetration is complete, there is a grave risk that the implement will continue penetrating deeply into the cavity and injure neighboring organ structure. If an unintended bodily member is injured by the point of the implement, unless an immediate and massive hemorrhage occurs, the injury may not become apparent until long after completion of the surgery. At a minimum, such an injury will delay a patient's recovery and may seriously endanger the patient's health. Corrective surgery may be required.
Some aspects of the dangers presented by the sharpened point of a penetrating implement have been previously recognized by those skilled in the field of surgical puncturing instruments.
U.S. Pat. No. 1,213,001 for example, positions a flat rubber cup along the outside of a cannula to limit the depth of trocar penetration. Additionally, a section of the proximal end trocar shaft is threaded whereby a threaded runner or lock-nut may be moved along the threaded shaft section to vary the extent by which the trocar point will protrude beyond the distal end of the cannula.
Similarly, U.S. Pat. No. 3,613,684, although using a trocar with a blunt, rounded tip, discloses an adjustible collar which fits around the exterior circumferential surface of the trocar shaft. The collar limits the extent of penetration of the trocar into a patient's body and provides a surgeon with a visual indication of the extent of penetration.
Another instrument, disclosed in U.S. Pat. No. 3,817,250, has a puncturing needle for performing a tracheostomy. The puncturing needle passes through the proximal end of a wide collar. The distal end of the collar forms a bearing surface against the neck of a patient at an acute angle to the longitudinal axis of the needle, thereby limiting the extent of penetration of the puncturing needle into the patient.
Devices such as cannula cups and collars are intended to be set prior to use to limit penetration into a bodily cavity to a single, fixed depth. The depth of penetration necessary to reach the inside of an anatomical cavity or to puncture an organ inside an anatomical cavity differs, however, for different organs. The depth of penetration necessary to reach a particular organ also differs among patients, being influenced by factors such as age, degree of development, obesity, sex, and previous medical experience. An instrument providing a fixed depth of penetration is, therefore, unsuitable for general surgical use because, for different patients, different thicknesses of tissue lie between the surface skin and the interior wall of an anatomical cavity. Even if the position of cannula collar is adjustable, the instrument provides no advance assurance that a particular setting will be adequate to permit the implement to reach the organ desired or that the depth of penetration will prevent the implement from penetrating too far into a cavity or organ and injuring neighboring anatomical members. Moreover, the collars only indicate the preset limit upon the depth of penetration and fail to provide a surgeon with a contemporaneous indication of whether the implement has successfully punctured the desired cavity after it has reached the preset limit of penetration. Some instruments have attempted to address the danger created by excessive penetration by providing a graduated scale on the cannula to indicate to a surgeon actual depth reached by the sharpened implement point. The visual indication provided, however, is independent of the depth of penetration necessary to reach a particular organ. Other instruments, the spinal epidural anesthetic needle taught in U.S. Pat. No. 4,215,699 for instance, rely upon changes of relative pressure differentials communicated to a sealed testing device chamber at the proximal end of the instrument to determine the location of the penetrating implement tip. Although the latter instrument provides a contemporaneous indication when the needle tip reaches a desired depth and a different indication when excessive penetration occurs, it is limited in use to the subarachnoid space. Both types of instruments rely upon a visual indication to appraise a surgeon about the relative depth of penetration; they provide only marginal protection against excessive penetration and no protection against post-penetration injury to the patient from inadvertent contact between neighboring organs and the sharp tip of the penetration implement.
Furthermore, none of the presently available surgical instruments provide protection to a patient against the sharp point of the penetrating implement after the implement has successfully penetrated a cavity. Until the point of the implement is withdrawn from a wound by retraction into the cannula, the possibility of an inadvertent contact between the point of the implement and other organs or membranes creates a serious risk that the point will graze, cut or even puncture other internal members of the patient.
Often, a preliminary precautionary procedure is taken, particularly prior to penetration of the pelvic or abdominal cavities, in an effort to reduce the risk of injuring interior anatomical structures. After a small incision is made, a needle such as the Verres needle or a small diameter safety endoscope of the type disclosed in U.S. Pat. No. 4,254,762 for instance, is first used to puncture the cavity wall. A gas, CO.sub.2, is next introduced into the cavity to create pneumoperitoneum, causing the cavity wall to bulge outward and separate from the organ structure inside the cavity. Then, a larger implement such as a trocar may be used to puncture the cavity wall with a lower risk of injuring other organ structure subsequent to penetration. Despite this precautionary procedure, there are still significant incidents of injury to bowels, blood vessels, and omenta due to inadvertent contact with the sharp trocar blade.